1. Field of the Invention
The present invention relates to a detection/communication apparatus for detecting a state of each vehicle tire such as its air pressure and temperature, and transmitting data representative of the tire state from a radio transmitter provided on each tire to a receiver provided on a vehicle body. More particularly, the invention is concerned with techniques for making it possible to distinguish a non-mounted tire from other tires mounted on axles of the vehicle, without a particular operation by a vehicle operator.
2. Discussion of Related Art
JP-A-2000-203221 discloses a spare-tire air-pressure monitoring apparatus in which a transponder is provided within an air chamber of a spare tire so that an air pressure of the spare tire can be monitored. The transponder has an air pressure sensor for detecting the air pressure, an integrated circuit including a data storage for storing data representative of the detected air pressure, and a power source in the form of a storage battery. The transponder, covered with an elastic member such as a resin so as to be protected from being damaged, is adapted to transmit the stored data in response to a data-requesting signal transmitted from an external device to the transponder.
In the spare-tire air-pressure monitoring apparatus disclosed in the Japanese publication, it is possible to monitor or obtain the data representative of the air pressure of the spare tire, without requiring a vehicle operator to perform a particular operation. However, the transponder is inevitably moved within the air chamber of the spare tire during running of the vehicle, so that the movement of the transponder contributes to a vibration of the vehicle body.